In mobile communication, not only voice communication but also the access to the Internet, distribution/communication of electronic mails and images, and the like can be relatively easily performed. Therefore, the mobile communication is used by a large number of people because of its convenience. In recent years, further development for an increase in speed and capacity is expected. In a situation in which the second generation (2G) and the third generation (3G) cellular systems and wireless access systems such as a wireless LAN are diversified, as the next generation wireless network after the third generation, a system for carrying out multicast communication according to a multicast procedure “IGMP (Internet Group Management Protocol)/MLD (Multicast Listener Discovery)” in a integrated heterogeneous mobile wireless network, in which heterogeneous wireless access systems are integrated in a layer 2 base, is examined.
As an example of the system, there is “Handoff for multicast receiver that takes into account IGMP-Snooping” described in a Non-Patent Literature 1. An outline of the Non-Patent Literature 1 is explained below referring to FIGS. 11 to 13. FIG. 11 is a conceptual diagram of a structure of the conventional integrated heterogeneous mobile wireless network described in the Non-Patent Literature 1. FIG. 12 is a sequence chart for explaining a control operation for handoff carried out in the same sub-network in the integrated heterogeneous mobile wireless network shown in FIG. 11. FIG. 13 is a sequence chart for explaining a control operation for handoff carried out between different sub-networks in the integrated heterogeneous mobile wireless network shown in FIG. 11.
In FIG. 11, contents such as streaming data provided by a source (a transmission source: Multicast Sender) 701 of multicast communication are input to a multicast router (MR1). Under the multicast router (MR1) 201, a multicast router (MR2) 202 and a multicast router (MR3) 203 are arranged to provide a mobile terminal (MH: Mobile Host) 601 with multicast delivery.
A switch (SW1) 401 is connected to the multicast router (MR2) 202. The switch (SW1) 401 has an IGMP-Snooping (Internet Group Management Protocol-Snooping) function of connecting a wireless base station (Base Station: BS1) 501 and a wireless base station (BS2) 502 subordinate to the switch (SW1) 401 to the multicast router (MR2) 202.
A switch (SW2) 402 is connected to the multicast router (MR2) 203. The switch (SW2) 402 has an IGMP-Snooping function of connecting a wireless base station (BS3) 503 and a wireless base station (BS2) 504 subordinate to the switch (SW2) 402 to the multicast router (MR3) 203.
In this network, to increase speed of a handoff operation for a multicast receiver, agents 301 and 302 called MSAs (Mobility Support Agents) are arranged for respective sub-networks. In FIG. 11, the agent (MSA1) 301 is connected to the switch (SW1) 401 and the agent (MSA2) 302 is connected to the switch (SW2) 402.
A handoff control operation carried out in the network shown in FIG. 11 is explained below. First, a handoff control operation in the same sub-network is performed as shown in FIG. 12. In FIG. 12, the mobile terminal MH is receiving multicast data (Multicast Data) through a route of the multicast router MR1, the switch SW1, and the wireless base station BS1 (S1001). When the mobile terminal MH performs handoff to the wireless base station BS2 (S1002), the mobile terminal MH transmits in a wireless manner an IGMP report message (IGMP Report) to the wireless base station BS2 as soon as possible in a process in which the wireless base station BS1 is transmitting in a wireless manner multicast data (Multicast Data) received from the switch SW1 (S1003). This IGMP report message is communicated from the wireless base station BS2 to the switch SW1 (S1004).
When the switch SW1 receives the IGMP report message, the switch SW1 transfers the multicast data (Multicast Data) transmitted from the multicast router MR1 to both the wireless base stations BS1 and BS2 (S1005). Consequently, the mobile terminal MH can continuously receive the multicast data (Multicast Data) in a new location.
The mobile terminal MH transmits in a wireless manner an advertisement request message (Advertisement Request) to the wireless base station BS2 by broadcast (Broadcast). This advertisement request message is transferred to the agent (MSA1) through the switch SW1 (S1006). When the agent (MSA1) receives the advertisement request message, the agent (MSA1) delivers an advertisement message (Advertisement) including a network prefix by broadcast (Broadcast). This advertisement message (Advertisement) is delivered to the mobile terminal MH through the switch SW1 and the wireless base station BS2 (S1007).
When the mobile terminal MH receives the advertisement message (Advertisement), the mobile terminal MH compares a previous prefix and the prefix included in the advertisement (Advertisement) and judges whether a handoff form is handoff in the same sub-network or handoff between different sub-networks. When the mobile terminal MH judges that the handoff form is the handoff in the same sub-network, the mobile terminal MH transmits in a wireless manner an IGMP leave message (IGMP Leave) to give trigger for checking a port of a receiver present under the switch SW1 to the switch SW1. This IGMP leave message is transferred to the multicast router MR1 through the wireless base station BS2 and the switch SW1 (S1008).
When the multicast router MR1 receives the IGMP leave message, the multicast router MR1 transmits an IGMP query message (IGMP Query (Group Specific)) to check whether receivers are present under the wireless base stations BS1 and BS2. This IGMP query message is transferred from the switch SW1 to both the wireless base station sBS1 and BS2 (S1009).
When the mobile terminal MH receives the IGMP query message, the mobile terminal MH transmits in a wireless manner an IGMP report message (IGMP Report) to the wireless base station BS2. This IGMP report message is communicated from the wireless base station BS2 to the switch SW1 (S1010). Consequently, the switch SW1 continuously delivers the multicast data (Multicast Data) to a port to which the wireless base station BS2, which is a new location of the mobile terminal MH, is connected. On the other hand, because there is no response to the IGMP query message from a port to which the wireless base station BS1, which is a previous location of the mobile terminal MH, is connected, the switch SW1 stops the distribution of the multicast data (Multicast Data) to the port to which the wireless base station BS1 is connected (S1011).
A handoff control operation between different sub-networks is performed as shown in FIG. 13. In FIG. 13, the mobile terminal MH is receiving multicast data (Multicast Data) through a route of the multicast routers MR1 and MR2, the switch SW1, and the wireless base station BS2 (S1011). When the mobile terminal MH performs handoff to the wireless base station BS3 (S1012), the mobile terminal MH transmits in a wireless manner an IGMP report message (IGMP Report) to the wireless base station BS3 as soon as possible in a process in which the wireless base station BS2 is transmitting in a wireless manner multicast data (Multicast Data) received from the switch SW1 (S1013). This IGMP report message is communicated from the wireless base station BS3 to the switch SW3 and the multicast router MR3 (S1014).
When the multicast router MR receives the IGMP report message from the multicast router MR3, the multicast router MR1 delivers the multicast data (Multicast Data) to both the multicast routers MR2 and MR3 (S1015). Consequently, the mobile terminal MH can continuously receive the multicast data (Multicast Data) in a new location.
The mobile terminal MH transmits in a wireless manner an advertisement request message (Advertisement Request) to the wireless base station BS3 by broadcast (Broadcast). This advertisement request message is transferred to the agent (MSA2) through the wireless base station BS3 and the switch SW2 (S1016). When the agent (MSA2) receives the advertisement request message, the agent (MSA2) delivers an advertisement message (Advertisement) including a network prefix by broadcast. This advertisement message (Advertisement) is delivered to the mobile terminal MH through the switch SW2 and the wireless base station BS3 (S1017).
When the mobile terminal MH receives the advertisement message (Advertisement), the mobile terminal MH updates an address (S1018) because handoff between different sub-networks is performed and transmits in a wireless manner a leave request message (Leave Request) to the agent MSA1 in a sub-network at a previous location. This leave request message (Leave Request) is transferred to the agent MSA1 through the wireless base station BS3, the switch SW2, the multicast routers MR3, MR1, and MR2, and the switch SW1 (S1019).
The agent MSA1 in the sub-network in the previous location transmits an IGMP leave message (IGMP Leave) to the multicast router MR2 through the switch SW1 as a response (S1020). When the multi-cast router MR2 receives the IGMP leave message (IGMP Leave), the multicast router MR2 transmits an IGMP query message (IGMP Query (Group specific)) to check whether a receiver is present under the wireless base station BS2. This IGMP query message is transferred from the switch SW1 to the wireless base station BS2 (S1021). However, since there is no receiver, no response is received. Consequently, both the switch SW1 in the previous location and the multicast router MR2 stop the distribution of the multicast data (Multicast Data). The mobile terminal MH can continue to receive the distribution of the multicast data (Multicast Data) in a new location through a distribution route of the multicast router MR3, the switch SW2, and the wireless base station BGS3 (S1022).
As described above, in the conventional integrated heterogeneous mobile wireless network shown in FIG. 11, the IGMP report message is transmitted immediately after movement to realize a reduction in a delay time until the start of multicast packet reception after the movement. It is identified whether handoff is the handoff in the same sub-network or the handoff between the different sub-networks from broadcast information (Advertisement). The mobile terminal directly transmits the IGMP leave message (IGMP-Leave) when the handoff is the handoff in the same sub-network and transmits the IGMP leave message (IGMP-Leave) in cooperation with the agent MSA when the handoff is the handoff between the different sub-networks. In this way, a reduction in a delay time until the stop of the distribution of a multicast packet in the previous location wireless base station is realized.
Non-Patent Literature 1: Yuki Moritani, Kensho Matsumoto, Ken-ichi Yamasaki “Handoff for a multicast receiver that takes into account IGMP-Snooping” The Institute of Electronics, Information and Communication Engineers Transaction (NS2003-104, NS2003-70, CS2003-79 (2003-09), FIGS. 1 to 3)